Are you pregnant? I had the rhogam shot with my last two pregnancies at 28 weeks. My husband is postive, so there's a chance the baby could have been positive.Both of mine were A- like me. If the baby's blood gets in your system, your body will view it as something to attack (something along those lines). I have since learned that the shot is not necessary and I will not do it for future pregnancies. There are other moms who do not get the shot and are fine.